Type I fimbriae are important for the urovirulence of E. coli, because they mediate adhesion, stimulate a mucosal immune response and mediate interactions with phagocytes. Experimental studies indicate the importance of type 1 fimbriae, but previous epidemiological studies found no correlation, perhaps because of the virtual ubiquity of the fim (type 1) gene cluster. Allelic variants of the gene for the FimH adhesin subunit that significantly alter the receptor-binding phenotype of E. coli have recently been discovered. Their distribution suggests that certain phenotypes offer a selective advantage in the urinary tract. This hypothesis is supported by preliminary animal studies. The effects of the expression of different fimH allelic variants on the ability of E. coli to colonize the mouse urinary tract will be studied. Isogenic E. coli strains will be inoculated into mouse bladders and infection studied by quantitative cultures and histopathology. We will identify the murine uroepithelial cell receptor(s) for E. coli expressing different fimH alleles. Preliminary studies lead us to focus on the asymmetrical unit membrane plaques (AUMs) of transitional epithelium and their constituent proteins, the uroplakins. In vitro and in vivo adhesion and adhesion inhibition assays (using uroplakin-specific antibodies) will be performed to confirm whether these molecules are the type 1 receptors. We will study the recruitment of leukocytes into the urinary tract mucosa of infected mice. The adhesion, ingestion and calling of E. coli by human and mouse peripheral blood PMN will be quantified and extracellular and intracellular release of oxygen metabolites will be measured. We will characterize the induction of cytokine production in urinary tract mucosa of mice infected with a recombinant E. coli strain exhibiting an M\H type 1 fimbrial phenotype typical of UTI isolates. When the basic responses have been characterized, we will determine whether qualitatively or quantitatively different responses are elicited by E. coli expressing different "fimH alleles. Production of inflammatory and regulatory cytokines will be measured by ELISAs and/or message will be measured by. RT-PCR. Cellular source(s) of cytokines will be determined by immunocytochemistry. The long-term goal of this research is to understand the role of type 1 fimbriae in the pathogenesis of UTIs to eventually enhance procedures for treatment or prevention.